Should OT teams prioritize machine identity governance before adding more authentication factors?

Why machine identity governance has to come first in OT

Authentication factors only help when the identity behind the factor is already well understood and tightly bounded. In OT environments, machine identity governance establishes that boundary by defining ownership, scope, and retirement conditions for each identity before any additional factor is layered on. Without that foundation, stronger authentication can protect a poorly governed access path instead of fixing it.

Machine identities in OT often outlive the systems, integrations, or projects that created them. That creates standing access, ambiguous ownership, and hidden trust paths across plant, engineering, and vendor-connected environments. A useful starting point is to treat machine identity as an operational asset with a lifecycle, not as a one-time login mechanism, and to anchor that view in Identity Convergence Guide and Service Account Security Guide.

That is why governance answers the first-order questions: what the identity represents, what systems it may reach, what conditions justify its continued use, and who can revoke it. In practice, OT teams should care less about adding another factor and more about eliminating orphaned, shared, or over-scoped machine access that an attacker or contractor could abuse later.

Authentication then becomes a reinforcement control. If the identity is already inventoried, assigned, and bounded, factors such as certificates, mutual TLS, or token-based authentication strengthen the trust model. If the identity is not governed, those same factors mainly make access harder to operate while leaving excess privilege and stale access untouched. For the underlying lifecycle and ownership model, NHI Lifecycle Management Guide and NHI Ownership and Accountability Guide are the relevant anchors.

Risk and Threat Considerations

In OT, weak machine identity governance creates a durable exposure because the same access path can be reused across long equipment lifecycles, vendor support flows, and plant-to-enterprise integrations. Attackers and insiders do not need a new factor if they can inherit an identity that was never properly retired, scoped, or monitored. That is why the access model itself is the risk surface, not just the login ceremony.

Failure mechanism: Shared, stale, or unowned machine identities accumulate permissions over time, and extra authentication factors are attached to the same unmanaged trust relationship instead of replacing it. If a credential, certificate, or token remains valid after its business purpose has ended, it can still be used for unauthorized OT reach.

Impact: The result is persistent access, harder incident containment, and a larger blast radius when an identity is compromised. In an OT setting that can translate into unauthorised reach into engineering tools, historians, remote maintenance paths, or other high-value systems, which is why the OT threat model in NIST SP 800-82 Rev 3, OT Security Guide matters here.

Practitioner Guidance

What to prioritise: Start with an identity inventory that distinguishes human access from machine access, and require an owner, purpose, expiry condition, and target scope for each machine identity. If you cannot name the owner or the assets it may reach, it is not ready for stronger authentication.

What to verify: Confirm that revocation is operational, not theoretical. A factor is only useful if teams can actually disable the identity, rotate the secret or certificate, and prove the old path no longer works across OT and adjacent IT environments.

What good looks like: Each machine identity has a clear business and technical owner, a documented reach boundary, a refresh or retirement rule, and a measurable review cadence. At that point, adding authentication factors improves assurance instead of masking governance gaps.

Practitioner takeaway: In OT, authentication should harden a governed identity model, not compensate for one that is still opaque, over-scoped, or effectively permanent.

Related resources from NHI Mgmt Group

• How should CIOs and CISOs prioritize machine identity management alongside user authentication and cloud IAM governance?
• Why does giving users control over adding authentication factors change the MFA operating model for identity teams?
• When does a machine identity become a compliance problem?
• Why is it important to integrate identity and data governance?